U.S. patent number 6,999,169 [Application Number 10/327,872] was granted by the patent office on 2006-02-14 for spectrometer.
This patent grant is currently assigned to Yokogawa Electric Corporation. Invention is credited to Makoto Komiyama, Kenji Ogino, Raiju Okada, Shuuhei Okada, Yoshihiro Sanpei, Yasuyuki Suzuki.
United States Patent |
6,999,169 |
Sanpei , et al. |
February 14, 2006 |
Spectrometer
Abstract
The present invention is intended to realize a spectrometer
which improves the wavelength resolution without being affected by
the pitch of the photodiode array. The present invention is
characterized by a spectrometer which comprises a wavelength
dispersion device spectrally dividing the measured light beam and a
photodiode array composed of a plurality of photodiodes that detect
the spectrally divided light beams by the wavelength dispersion
device and output photocurrents, and performs measurement using the
outputs of the photodiode array; providing a deflecting means that
deflects the measured light beams and changes the position where
the measured light beams are detected by the above photodiode
array, and measuring the characteristics of the measured light beam
from the measured results for different deflection amounts.
Inventors: |
Sanpei; Yoshihiro (Musashino,
JP), Komiyama; Makoto (Musashino, JP),
Ogino; Kenji (Musashino, JP), Suzuki; Yasuyuki
(Musashino, JP), Okada; Raiju (Musashino,
JP), Okada; Shuuhei (Musashino, JP) |
Assignee: |
Yokogawa Electric Corporation
(Tokyo, JP)
|
Family
ID: |
19190813 |
Appl.
No.: |
10/327,872 |
Filed: |
December 26, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20030128359 A1 |
Jul 10, 2003 |
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Foreign Application Priority Data
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Jan 10, 2002 [JP] |
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2002-002991 |
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Current U.S.
Class: |
356/328 |
Current CPC
Class: |
G01J
3/2803 (20130101) |
Current International
Class: |
G01J
3/28 (20060101) |
Field of
Search: |
;356/308,328,334 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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61-270736 |
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Dec 1986 |
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JP |
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01-197617 |
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Aug 1989 |
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JP |
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03-102229 |
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Apr 1991 |
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JP |
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05-134275 |
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May 1993 |
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JP |
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11-194280 |
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Jul 1999 |
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JP |
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Primary Examiner: Smith; Zandra V.
Assistant Examiner: Geisel; Kara
Attorney, Agent or Firm: Westerman, Hattori, Daniels &
Adrian, LLP
Claims
What is claimed is:
1. A spectrometer comprising: a wavelength dispersion device
spectrally dividing the measured light beam; a photodiode array
composed of a plurality of photodiodes that detect the spectrally
divided light beams by the wavelength dispersion device and output
photocurrents for performing measurement; and a deflecting means
that deflects said measured light beam and changes the position
where said measured light beam is detected by said photodiode
array, wherein the characteristics of said measured light beam are
determined from the measured results for different deflection
amounts, and wherein said wavelength dispersion device is a grating
provided in the longitudinal direction of an optical fiber
core.
2. A spectrometer in accordance with claim 1, wherein said
deflecting means is a piezoelectric actuator which is mounted along
the longitudinal direction of the optical fiber on which a grating
is provided and expands or contracts the optical fiber.
3. A spectrometer comprising: a wavelength dispersion device
spectrally dividing the measured light beam; a photodiode array
composed of a plurality of photodiodes that detect the spectrally
divided light beams by the wavelength dispersion device and output
photocurrents for performing measurement; and a deflecting means
that deflects said measured light beam and changes the position
where said measured light beam is detected by said photodiode
array, wherein the characteristics of said measured light beam are
determined from the measured results for different deflection
amounts, and wherein said wavelength dispersion device is a grating
provided on an optical waveguide.
4. A spectrometer in accordance with claim 3, wherein said
deflecting means is a pair of electrodes which are installed on
both sides of the optical waveguide on which a grating is provided
counter to each other and deflects the measured light beam using
the electro-optic effect.
5. A spectrometer in accordance with any one of claims 1,2,3, and
4, wherein said deflecting means causes deflection within one pitch
that is the sum of the width of a photodiode and the width of a
dead zone between adjacent photodiodes on said photodiode array.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spectrometer in which the
wavelength resolution is improved without being affected by the
pitch of a photodiode array.
2. Description of the Prior Art
Wavelength Division Multiplexing (WDM) communication is one type of
optical communication systems which transmit optical signals by
using optical fibers. This WDM communication is a communication
system which transmits multiple optical signals of different
wavelengths using a single optical fiber. Multiple optical signals
of different wavelengths are also called WDM signals. In many
cases, each optical signal in WDM signals is counted, for example,
in ascending order of wavelength (that is, starting at the shortest
wavelength) as channel 1, channel 2, etc.
The spectrometer is a measuring equipment that obtains the
wavelength spectrum of the light being measured (hereafter called
`measured light beam`) using a wavelength dispersion device,
determines the optical power existing in an arbitrary wavelength
band, and measures the characteristics of the measured light beam
using this determined optical power. This spectrometer is used for
measuring WDM signals very frequently, and obtains the wavelength
spectrum of input WDM signals and determines optical signal levels
and wavelengths and the like for each channel using the optical
power determined.
FIG. 1 is a configuration drawing indicating an embodiment of
spectrometers that measure such WDM signals. In FIG. 1,
spectroscope 10 is called a polychromator system into which WDM
signals, the measured light beams, are input and which sends out
the output corresponding to an optical power existing in an
arbitrary wavelength band as a measured signal.
Spectroscope 10 is composed of optical fiber 11, collimating lens
12, grating 13 that is a wavelength dispersion device, focusing
lens 14, mirror 15, and photodiode array module 16 (hereafter
abbreviated as "PDM").
Optical fiber 11 is a transmission line for making the measured
light beam incident to spectroscope 10. Collimating lens 12 is
installed counter to the optical output window of optical fiber 11
and emits measured light beam 100 output from optical fiber 11
after collimating it.
Grating 13 is installed oblique to collimating lens 12 to diffract
the emitted light beam from collimating lens 12 by a desired angle.
Then, grating 13 emits measured light beam 100 into a spectrum
deflecting the light beam to different angles for every wavelength.
Focusing lens 14 is provided on the optical path of emitted light
from grating 13 and focuses the emitted light. Mirror 15 is
installed to reflect the emitted light from focusing lens 14 in the
desired direction.
PDM 16 is placed in the position at which measured light beam 100
reflected from mirror 15 focuses. On PDM 16, a PD array is formed,
in which a plurality of strip-type or spot-type photodiodes
(hereafter abbreviated as "PD") is arranged. Each of these PDs
generates a current (photocurrent) corresponding to the optical
power of incident measured light beam 100 and outputs these
photocurrents as measured signals of spectroscope 10.
In addition, a wavelength is assigned to each PD in advance. The
assignment of wavelength corresponds to each position at which
measured light beam 100 is deflected for each wavelength by grating
13 and focused on the PD array.
Control unit 20 comprises driving means 21, memorizing means 22,
and calculating means 23. Driving means 21 changes over connections
to each PD of PDM 16 in turn, reads measured signals from each PD
in turn, for example, in ascending order of wavelength from the
shortest one, and outputs each measured signal after converting
them to the desired signals. Memorizing means 22 stores signals
output from driving means 21 in turn. Calculating means 23 reads
signals stored in memorizing means 22, determines the optical
signal levels, wavelengths, or the like of measured light beam 100,
and outputs the calculated results.
Operation of the spectrometer shown in FIG. 1 will now be
described. Assume that different wavelengths of wavelength A and
wavelength B are multiplexed in measured light beam 100. Measured
light beam 100 emitted from optical fiber 11 is collimated with
collimating lens 12. Measured light beam 100 transmitted through
collimating lens 12 is incident to grating 13, and is spectrally
divided into measured light beams 100A and 100B for each wavelength
of .lamda.A and .lamda.B with this grating 13. Although measured
light beams 100A and 100B spectrally divided with grating 13 are
focused on the PD array of PDM 16 by focusing lens 14 and mirror
15, the positions of focusing the optical spot are shifted
corresponding to wavelengths .lamda.A and .lamda.B of measured
light beams 100A and 100B. Photocurrents are output from each PD
respectively. As described above, spectroscope 10 does not contain
mechanical moving parts and can operate stably for a long time.
Driving means 21 changes over connections to each PD of PDM 16 in
turn, reads photocurrents generated in each PD in turn starting at
the shortest wavelength, and converts these read photocurrents to
voltages. In addition, since the signals converted to voltages are
analog signals, driving means 21 converts these analog signals to
digital signals and stores them in memorizing means 22 in the order
of reading from each PD. Calculating means 23 determines the
optical signal levels and peak wavelengths of each channel using
digital signals stored in memorizing means 22 and wavelengths
assigned to each PD, and outputs these calculation results. The
output unit not shown displays the calculation results output from
calculating means 23, for example, on the screen of the display
unit or outputs them to external equipment not shown.
Subsequently, the action of calculating means 23 for determining
the optical signal levels and peak wavelengths of each channel will
now be described in detail. FIG. 2 schematically shows that part of
the PD array is irradiated with measured light beam 100A. In FIG.
2, PD16a to PD16e are arranged in the direction in which measured
light beam 100 is spectrally divided for wavelengths .lamda.A and
.lamda.B by grating 13. Wavelengths of .lamda..sub.a to
.lamda..sub.e (.lamda..sub.a<.lamda..sub.b< . . .
<.lamda..sub.e) are assigned to each PD of 16a to 16e
respectively.
In addition, the PD array is not formed such that PD16a to PD16e
that generate photocurrents are arranged without gaps in the
direction of arrangement, but is formed such that PD16a of width
.DELTA.p, a dead zone of width .DELTA.q, PD16b of width .DELTA.p .
. . are arranged in this order in the direction of arrangement.
Therefore, the width of one pitch is the sum of the width .DELTA.p
of each PD of PD16a to PD16e and the width of dead zone .DELTA.q.
Although each of PD16a to PD16e has the width .DELTA.p, the center
positions of each PD in the direction of arrangement are generally
made to correspond to assigned wavelengths .lamda..sub.a to
.lamda..sub.e respectively.
From one side or both sides of each of PD16a to PD16e,
photocurrents are output by signal wires not shown.
If measured light beam 100A has a line spectrum such as laser
light, the optical spot of measured light beam 100A formed on the
PD array takes the shape of an ellipse or circle, whose optical
power shows a Gaussian distribution. In this case, it is assumed
that the center of measured light beam 100A is in the vicinity of
PD16c. FIG. 3 indicates the outputs of each of PD16a to PD16e
stored in memorizing means 22. The abscissa shows wavelengths
.lamda..sub.a to .lamda..sub.e assigned to each of PD16a to PD16e,
and the ordinate shows the relative outputs of PD16a to PD16e. The
outputs of PD16a to PD16e are represented by P.sub.a to P.sub.e.
Since the center of measured light beam 100A exists in the vicinity
of PD16c, it is apparent that the output P.sub.c from PD16c is
larger than any of the other outputs P.sub.a, P.sub.b, P.sub.d, and
P.sub.e. In addition, .DELTA..lamda. shows a value in wavelength
converted from the width of one pitch of the PD array.
The response of spectroscope 10 to a line spectrum input to it is
approximated as a Gaussian distribution and the peak wavelength
.lamda..sub.peak of measured light beam 100A can be expressed by
equation (1). .lamda..sub.peak=.lamda..sub.0+.delta..lamda. (1)
where .lamda..sub.0 is the wavelength .lamda..sub.c assigned to
PD16c whose optical power is closest to the peak optical power and
.delta..lamda. represents the difference between the peak
wavelength .lamda..sub.peak and the wavelength .lamda..sub.c
assigned to PD16c whose optical power is closest to the peak
optical power. The value .delta..lamda. can also be expressed from
equation (2) using the distance .delta.x between the center of
PD16c and the center of the optical spot of measured light beam
100A in FIG. 2, and the ratios of the output of PD16c nearest to
the center of the optical spot of measured light beam 100A to each
output of PD16b and PD16d both adjacent to PD16c.
.delta..times..times..lamda..times..delta..times..times..times..DELTA..la-
mda..DELTA..times..times..DELTA..times..times..times..DELTA..times..times.-
.lamda..function..function. ##EQU00001## where P.sub.0 corresponds
to the output P.sub.c of PD16c nearest to the peak optical power,
and P.sub.-1 and P.sub.+1 correspond to P.sub.b and P.sub.d
respectively.
The optical signal level P.sub.sig of measured light beam 100A can
be determined as shown in equation (3) using the integral of the
spectrum spread over the PD array, or the sum of output values
P.sub.b, P.sub.c, and P.sub.d from three PDs, that is, PD16b,
PD16c, and PD16d near the peak optical power:
P.sub.sig=.alpha.(.delta.x)(P.sub.-1+P.sub.0+P.sub.+1) (3) where
.alpha.(.delta.x) is a function taking the distance between the
center of the optical spot and the center of PD16c as a variable.
This is because the value to be added differs depending on the
distance between the center of the optical spot and the center of
PD16c. This is a function determined by the diameter of the optical
spot and the width of one pitch of the PD array.
Since operations in which calculating means 23 determines the
optical signal level and peak wavelength of measured light beam
100B in the other channel are similar to the above, description of
them will be omitted.
The wavelength resolution of spectroscope 10 depends on the size of
the optical spot formed on the PD array. To improve the wavelength
resolution, it is sufficient to make the optical spot size smaller
(to sharpen the response spectrum) and focus it to one pitch of the
PD array or less.
FIG. 4 shows the outputs of PD16a to PD16e, P.sub.a to P.sub.e, in
the case of, for example, improving the wavelength resolution by
taking the optical spot size to about one pitch of PD16a to PD16e.
The wavelength resolution represents the performance that can
identify channels if each channel is brought near. In FIG. 4, the
same objects as those in FIG. 3 are given the same signs and so
description of them is omitted.
FIG. 4 (a) indicates the case where the peak optical power of
measured light beam 100A exists close to the center of PD16c. In
FIG. 4 (a), outputs P.sub.b and P.sub.d that can be detected with
PD16b and PD16d both adjacent to PD16c which is nearest to the peak
become extremely small. For this reason, these are easily subjected
to influences of noise and it is hard to determine the optical
signal level and the peak wavelength accurately.
Also, FIG. 4 (b) indicates the case where the peak optical power of
measured light beam 100A exists at about the mid point between
PD16c and PD16d (dead zone). In FIG. 4 (b), since the major part of
the optical power is concentrated in the dead zone, PD16c and
PD16d, the output P.sub.b that can be detected with PD16b becomes
extremely small. For this reason, the output P.sub.b is easily
subjected to influences of noise and it is hard to determine the
optical signal level and the peak wavelength accurately.
As described above, when the optical spot is made small to improve
the wavelength resolution, the outputs of PDs to be used for
calculation become small and are easily subjected to influences of
noise. Accordingly, it becomes difficult to measure the optical
signal level and the peak wavelength accurately. To reduce the
influences of noise, it is sufficient to make the pitch of the PD
array small. However, the types of generally available PD arrays
are limited and it is not easy to change the shape such as changing
the pitch of a PD array.
SUMMARY OF THE INVENTION
The purpose of the present invention is to realize a spectrometer
in which the wavelength resolution is improved without being
affected by the pitch of a photodiode array.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a configuration drawing indicating an embodiment of the
conventional spectrometer.
FIG. 2 is a schematic drawing showing part of a photodiode
array.
FIG. 3 is a graph showing an output characteristic indicating an
example of the relationship between a photodiode array and
photodiode outputs.
FIG. 4 shows graphs representing output characteristics indicating
examples of the relationship between a photodiode array and
photodiode outputs in the case where the optical spot of measured
light beam 100A is small.
FIG. 5 is a configuration drawing indicating a first embodiment of
the present invention.
FIG. 6 shows graphs representing output characteristics indicating
examples of the relationship between a photodiode array and
photodiode outputs, in one of which calculating means 45 in a
spectrometer shown in FIG. 5 carries out the sorting of the data of
groups 1 and 2 in the order of the wavelength values.
FIG. 7 is a configuration drawing indicating a second embodiment of
the present invention.
FIG. 8 is a configuration drawing indicating a third embodiment of
the present invention.
FIG. 9 is a configuration drawing indicating a fourth embodiment of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention will now be described
below with reference to the drawings.
FIG. 5 is a configuration drawing indicating a first embodiment of
the present invention. In FIG. 5, the same objects as those in FIG.
1 are given the same signs and so description of them is omitted.
In FIG. 5, spectroscope 30 is provided instead of spectroscope 10
and electro-optic beam deflector 31, which is one type of
deflecting means that deflects measured light beams 100A and 100B,
is newly installed between mirror 15 and PDM 16.
Electro-optic beam deflector 31 is a light deflector using the
effect that the refractive index of a medium varies with an applied
DC or applied electric field whose frequency is sufficiently lower
than the optical frequency (electro-optic effect) by receiving a
current or a voltage from outside. For example, deflection can be
performed by changing the emitting direction of a prism by changing
its refractive index or forming a linear phase distribution in a
cross sectional plane orthogonal to the light wave propagating
direction by refractive index changes generated in a medium by the
electro-optic effect.
Control unit 40 is provided instead of control unit 20 and is
composed of synchronizing means 41, driver 42, driving means 43,
memorizing means 44 and calculating means 45. Synchronizing means
41 outputs the synchronizing signals. Driver 42 applies a desired
voltage to electro-optic beam deflector 31 according to
synchronizing signals of synchronizing means 41. Driving means 43
changes over connections with each PD of PDM 16 in turn according
to synchronizing signals of synchronizing means 41, reads the
measuring signals of each PD in turn, for example, starting at the
shortest wavelength, and outputs the measured signals after
converting them to the desired signals. Memorizing means 44 stores
the signals output from driving means 43 in turn and can hold the
signals output from driving means 43 for an amount of up to several
times of output. Calculating means 45 reads the signals stored in
memorizing means 44 for an amount of up to several times of output,
determines the optical signal level, the wavelengths, and the like
of measured light beam 100 based on these read-out signals, and
outputs the calculated results.
Operation of the spectrometer shown in FIG. 5 will now be
described. Synchronizing means 41 outputs the first time
synchronizing signal to driver 42 and driving means 43. Driver 42
deflects measured light beams 100A and 100B reflected by mirror 15
by the desired amount in the arranging direction of the PD array in
PDM 16, by applying a voltage V.sub.a to electro-optic beam
deflector 31 based on the synchronizing signal. Here, it is assumed
that the centers of the optical spots of measured light beams 100A
and 100B irradiate the same positions on the PD array of the
spectroscope shown in FIG. 1. The deflected measured light beams
100A and 100B focus on the PD array respectively and photocurrents
are output from each PD as the measuring signals.
Driving means 43 changes over the connection of each PD of PDM 16
based on the synchronizing signal and reads photocurrents generated
in each PD in ascending order of wavelength starting at the
shortest wavelength. Driving means 43 further converts these
photocurrents to voltages, converts the analog signals converted to
voltages to digital signals, and stores them in memorizing means
44. Digital signals stored in memorizing means 44 by the first time
synchronizing signal are collected as the group 1 data.
Subsequently, synchronizing means 41 outputs the second time
synchronizing signal to driver 42 and driving means 43 again.
Driver 42 applies voltage V.sub.b to electro-optic beam deflector
31 based on this synchronizing signal and deflects measured light
beams 100A and 100B reflected by mirror 15 by the desired amount in
the arranging direction of the PD array. However, measured light
beams 100A and 100B are deflected so that they irradiate the
position deflected by a 1/2 pitch toward longer wavelengths from
the position on the PD array irradiated with measured light beams
100A and 100B by the first time synchronizing signal. Deflected
measured light beams 100A and 100B focus on the PD array
respectively and photocurrents are output from each PD as the
measured signals.
Driving means 43 changes over the connection of each PD of PDM 16
based on the synchronizing signal and reads the photocurrents
generated in each PD in ascending order of wavelength starting at
the shortest wavelength. Driving means 43 further converts these
photocurrents to voltages, converts the analog signals converted to
voltages to digital signals, and stores them in memorizing means
44. In this case, these signals are stored in a region other than
that for group 1 data stored in memorizing means 44 based on the
first time synchronizing signal. Digital signals stored in
memorizing means 44 by the second time synchronizing signal are
collected as the group 2 data.
Calculating means 45 reads the group 1 and group 2 data from
memorizing means 44 and carries out sorting of the group 1 and
group 2 data in the order of the wavelength values. Through this
operation, the group 1 and group 2 data become the data for
interpolating each other and thus measured signals similar to those
in the case of measurement with a 1/2 pitch on the PD array of PDM
16 are obtained.
FIG. 6 shows graphs indicating the outputs of each of group 1 and
group 2 data and outputs of the interpolated data in the
spectrometer shown in FIG. 5. In FIG. 6, the same objects as those
in FIG. 3 are given the same signs and so description of them is
omitted. However, in FIG. 6, only the data for PD16b to PD16d in
the vicinity of the peak are shown. Since, for the group 2 data,
the position of measured light beam 100A irradiation is deflected
by a 1/2 pitch toward the longer wavelength, the wavelengths
assigned to each of PD16b to PD16d are shifted toward the shorter
wavelength by a 1/2 pitch respectively. In FIG. 6, for the group 1
data, the outputs corresponding to PD16b to PD16d are given the
signs P1.sub.b to P1.sub.d respectively and represented with
symbols .cndot.; and for the group 2 data, the outputs
corresponding to PD16b to PD16d are given the signs P2.sub.b to
P2.sub.d respectively and represented with symbols x.
Calculating means 45 determines the optical signal level and peak
wavelength of measured light beam 100A using equations (1) to (3)
from the values of wavelengths in the vicinity of peak
.lamda..sub.c-.DELTA..lamda./2, .lamda..sub.c, and
.lamda..sub.d-.DELTA..lamda./2 and the outputs corresponding to
these wavelengths P2.sub.c, P1.sub.c and P2.sub.d based on the
interpolated data. However, the first term of the second line of
equation (2) becomes .DELTA..lamda./4 because measured light beam
100A is deflected by a 1/2 pitch and the pitch of the PD array is
reduced to 1/2.
Since the operations for determining the optical signal level and
the peak wavelength of measured light beam 100B are identical to
the above, description of them is omitted. In addition, since other
operations in the spectrometer shown in FIG. 5 are similar to those
in the spectrometer shown in FIG. 1, description of them is also
omitted.
As described above, the measurement of measured light beams 100A
and 100B is carried out by deflecting measured light beams 100A and
100B in the arranging direction of the PD array on PDM 16 with
electro-optic beam deflector 31, performing a series of operations
in which measured signals are acquired by driving means 43 two or
more times, and sorting these signals in order of wavelength
values. This enables measured signals obtained by sorting to be
acquired equivalent to the measurement with a pitch smaller than
one pitch, and thus measurement can be performed even if the
optical spot size of measured light beams 100A and 100B is made
smaller because the data whose detecting outputs are small and
which are easily subjected to influences of noise are not used.
Consequently, the optical signal level and the peak wavelength can
be measured with improved wavelength resolution.
Further, since electro-optic beam deflector 31 employs the
electro-optic effect without having mechanically moving parts,
spectroscope 30 can be operated stably for a long time.
FIG. 7 is a configuration drawing indicating a second embodiment of
the present invention. In FIG. 7, the same objects as those in FIG.
5 are given the same signs and so description of them and
indication in the drawing are both omitted. In FIG. 7, spectroscope
50 is provided instead of spectroscope 30 and mirror 51 instead of
mirror 15. In addition, piezoelectric actuator 52 is mounted
instead of a deflecting means, electro-optic beam deflector 31, so
that the actuator mechanically shifts the position of mirror 51 to
compose a deflecting means using piezoelectric actuator 52 and
mirror 51. A voltage is applied to piezoelectric actuator 52 from
driver 42. Piezoelectric actuator 52 generates a mechanical stress,
such as expansion or contraction, if a voltage is applied.
Operations of the spectrometer shown in FIG. 7 will now be
described. Driver 42 applies voltage Vc to piezoelectric actuator
52 based on the first time synchronizing signal, shifts
piezoelectric actuator 52 by the desired amount, and deflects
measured light beams 100A and 100B reflected by mirror 51 in the
arranging direction of the PD array on PDM 16. Here, it is assumed
that the center of the optical spot of measured light beams 100A
and 100B irradiates the same position as that on the PD array of
the spectrometer shown in FIG. 5. Further, driver 42 applies
voltage Vd to piezoelectric actuator 52 based on the second time
synchronizing signal, shifts piezoelectric actuator 52 by the
desired amount, and deflects measured light beams 100A and 100B
reflected by mirror 51 in the arranging direction of the PD array.
However, measured light beams 100A and 100B are deflected so that
their irradiating position on the PD array is shifted by a 1/2
pitch towards the longer wavelength from the position at which
measured light beams 100A and 100B irradiate on the PD array based
on the first time synchronizing signal.
Here, since operations other than applying voltages Vc and Vd to
piezoelectric actuator 52 based on the synchronizing signals and
deflecting reflected light from mirror 51 by the desired amount are
the same as those in the spectrometer shown in FIG. 5, description
of them is omitted.
As described above, measured light beams 100A and 100B are measured
by deflecting measured light beams 100A and 100B in the arranging
direction of the PD array on PDM 16 using mirror 51 and
piezoelectric actuator 52, performing a series of operations, in
which driving means 43 acquires measuring signals two or more
times, and sorting these signals in order of wavelength values.
This enables measured signals obtained by sorting to be acquired
similar to the measurement with smaller pitch than one pitch, and
thus measurement can be performed even if the optical spot size of
measured light beams 100A and 100B is made smaller because the data
whose detecting outputs are small and which are easily subjected to
influences of noise are not used. Consequently, the optical signal
level and the peak wavelength can be measured with improved
wavelength resolution.
FIG. 8 is a configuration drawing indicating a third embodiment of
the present invention. In FIG. 8, the same objects as those in FIG.
5 are given the same signs and so description of them and
indication in the drawing are both omitted. In FIG. 8, spectroscope
60 is provided instead of spectroscope 30. Spectroscope 60 also has
optical fiber 11, fiber grating 61 as the wavelength dispersion
device, lens 62, PDM 16 and piezoelectric actuator 63 as a driving
means. Fiber grating 61 includes a grating area formed by changing
the periodical refractive index in the longitudinal direction of
the optical fiber core.
Fiber grating 61 is connected with the emission end of optical
fiber 11 by, for example, fusion welding and measured light beam
100 is incident. Fiber grating 61 spectrally divides the incident
light to measured light beams 100A and 100B for each of wavelengths
.lamda.A and .lamda.B at grating area 61a in which the grating is
formed and emits them at different angles to the space from fiber
grating 61 itself for every wavelength of .lamda.A and .lamda.B.
Lens 62 is installed in the optical path of emitted light from
fiber grating 61 and focuses the emitted light. PDM 16 is mounted
so that its position is where measured light beams 100A and 100B
are focused by lens 62, and outputs photocurrents generated in each
PD. Piezoelectric actuator 63 is mounted by aligning its direction
of expansion or contraction with the longitudinal direction of
grating area 61a. In addition, a voltage is applied to
piezoelectric actuator 63 from driver 42.
Operations of the spectrometer shown in FIG. 8 will now be
described. Driver 42 applies voltage Ve to piezoelectric actuator
63 based on the first time synchronizing signal and expands or
contracts piezoelectric actuator 63 by the desired amount. This
also expands or contracts grating area 61a to which piezoelectric
actuator 63 is attached in the longitudinal direction. For this
reason, the period of the refractive index, which is provided for
grating area 61a to vary periodically, changes and so measured
light beams 100A and 100B emitted from grating area 61a are
deflected in the arranging direction of the PD array on PDM 16.
Here, it is assumed that the center of the optical spot of measured
light beams 100A and 100B irradiates the same position as that on
the PD array of the spectrometer shown in FIG. 5. Further, driver
42 applies voltage Vf to piezoelectric actuator 63 based on the
second time synchronizing signal, expands or contracts
piezoelectric actuator 63 by the desired amount, and deflects
measured light beams 100A and 100B in the arranging direction of
the PD array in a similar manner. However, measured light beams
100A and 100B are deflected so that their irradiating position on
the PD array is shifted by a 1/2 pitch towards the longer
wavelength from the position at which measured light beams 100A and
100B irradiate on the PD array based on the first time
synchronizing signal.
Here, since operations other than applying voltages Ve and Vf by
driver 42 to piezoelectric actuator 63 based on the synchronizing
signals and deflecting measured light beams 100A and 100B emitted
from grating area 61a, are the same as those in the spectrometer
shown in FIG. 5, so description of them is omitted.
As described above, measured light beams 100A and 100B are measured
by deflecting measured light beams 100A and 100B in the arranging
direction of the PD array on PDM 16 using piezoelectric actuator
63, performing a series of operations, in which driving means 43
acquires measuring signals two or more times, and sorting these
signals in order of wavelength. This enables measured signals to be
acquired similar to the measurement with smaller pitch than one
pitch, and thus measurement can be performed even if the optical
spot size of measured light beams 100A and 100B is made smaller
because the data whose detecting outputs are small and which are
easily subjected to influences of noise are not used. Consequently,
the optical signal level and the peak wavelength can be measured
with improved wavelength resolution.
FIG. 9 is a configuration drawing indicating a fourth embodiment of
the present invention. In FIG. 9, the same objects as those in FIG.
5 are given the same signs and so description of them and
indication in the drawing are both omitted. In FIG. 9, spectroscope
70 is provided instead of spectroscope 30. Spectroscope 70 also
includes optical fiber 11, waveguide grating 71 as the wavelength
dispersion device, lens 72, PDM 16 and electrodes 73a and 73b as a
deflecting means. Waveguide grating 71 includes a grating area
where the periodical refractive index change is mechanically formed
in the longitudinal direction of the optical waveguide. The optical
waveguide is composed of a medium having the electro-optical
effect, such as lithium niobate or the like.
Optical fiber 11 is a transmission line that makes measured light
beam 100 be incident to spectroscope 70. Measured light beam 100
emitted from the emission end of optical fiber 11 is incident to
waveguide grating 71. In this case, a lens or matching oil or the
like may be provided between optical fiber 11 and waveguide grating
71 to enable measured light beam 100 to be incident to waveguide
grating 71 efficiently.
Waveguide grating 71 spectrally divides the incident light to
measured light beams 100A and 100B for each of wavelengths .lamda.A
and .lamda.B at grating area 71a in which the grating is formed,
and emits them at different angles to the space from waveguide
grating 71 itself for every wavelength of .lamda.A and .lamda.B.
Lens 72 is installed in the optical path of the light emitted from
waveguide grating 71 and focuses the emitted light. PDM 16 is
mounted so that its position is where measured light beams 100A and
100B are focused by lens 72, and outputs photocurrents generated in
each PD. Electrodes 73a and 73b are mounted counter to each other
on both sides of grating area 71a. The shape of electrodes 73a and
73b should be that of a comb. Voltages are applied to electrodes
73a and 73b from driver 42 respectively.
Operations of the spectrometer shown in FIG. 9 will now be
described. Driver 42 applies voltage Vg to electrodes 73a and 73b
based on the first time synchronizing signal, changes the
refractive index of grating area 71a using the electro-optic
effect, and deflects measured light beams 100A and 100B emitted
from grating area 71a in the arranging direction of the PD array of
PDM 16 by the desired amount. Here, it is assumed that the center
of the optical spot of measured light beams 100A and 100B
irradiates the same position as that on the PD array of the
spectrometer shown in FIG. 5. Further, driver 42 applies voltage Vh
to electrodes 73a and 73b based on the second time synchronizing
signal, changes the refractive index of grating area 71a using the
electro-optic effect, and deflects measured light beams 100A and
100B emitted from grating area 71a in the arranging direction of
the PD array by the desired amount. However, measured light beams
100A and 100B are deflected so that their irradiating position on
the PD array is shifted by a 1/2 pitch towards the longer
wavelength from the position at which measured light beams 100A and
100B irradiate on the PD array based on the first time
synchronizing signal.
Here, since operations other than applying voltages Vg and Vh by
driver 42 to electrodes 73a and 73b based on the synchronizing
signals and deflecting measured light beams 100A and 100B emitted
from grating area 71a are the same as those in the spectrometer
shown in FIG. 5, description of them is omitted.
As described above, measured light beams 100A and 100B are measured
by deflecting measured light beams 100A and 100B in the arranging
direction of the PD array on PDM 16 using voltages Vg and Vh
applied to electrodes 73a and 73b, performing a series of
operations, in which driving means 43 acquires measuring signals
two or more times, and sorting these signals in order of wavelength
values. This enables measured signals to be acquired similar to the
measurement with a pitch smaller than one pitch, and thus
measurement can be performed even if the optical spot size of
measured light beams 100A and 100B is made smaller because the data
whose detecting outputs are small and which are easily subjected to
influences of noise are not used. Consequently, the optical signal
level and the peak wavelength can be measured with improved
wavelength resolution.
Further, the electro-optic effect brought by applying a voltage to
electrodes of waveguide grating 71 is adopted for deflection of
measured light beams 100A and 100B. Since the above deflecting
means has no moving parts, spectroscope 70 can be operated stably
for a long time.
Note that the present invention is not restricted to the
configurations mentioned above; the configurations shown below may
also be employed.
Although an example is shown in which measured light beam 100 is
multiplexed in two channels of wavelengths .lamda.A and .lamda.B,
any number of channels may be multiplexed.
In FIG. 5, although electro-optic beam deflector 31 is provided
between mirror 15 and PDM 16, the deflector may be installed
anywhere if the installing place exists before measured light beam
100 is incident to PDM 16, such as between optical fiber 11 and
lens 12 or between lens 12 and grating 13.
Also in FIG. 5, although the configuration in which the light beam
emitted from lens 14 is reflected by mirror 15 and detected by PDM
16, a configuration in which mirror 15 is not provided and PDM 16
is installed in a position where the light beam emitted from lens
14 is focused may be employed. Electro-optic beam deflector 31 can
be provided anywhere if the installing place exists before measured
light beam 100 is incident to PDM 16.
The configuration in which grating 13 is used as the wavelength
dispersion device in the spectrometers shown in FIG. 5 and FIG. 7
is indicated. However, that configuration may use a prism as the
wavelength dispersion device or may use both a prism and grating
13. The wavelength dispersion angles of a prism and grating 13 can
be matched by using both a prism and grating 13.
In the spectrometers shown in FIG. 5 and FIG. 7, a plane type
grating is used for grating 13. However, a concave type grating can
also be used. In addition, a configuration without using lens 12
and/or lens 14 may be adopted by using a concave type grating. This
enables PDM 16 to detect measured light beam 100 without
attenuation through lens 12 and/or lens 14.
In the spectrometers shown in FIG. 5 and FIG. 7 to FIG. 9, although
a transmission type optical system using lens 12 and/or 14, or 62
or 72 is shown, a reflection type optical system using a parabolic
mirror can also be used.
In the spectrometers shown in FIG. 5 and FIG. 7 to FIG. 9, a
configuration, in which deflection of measured light beams 100A and
100B is carried out with the deflection amount of a 1/2 pitch
towards longer wavelengths, is indicated. However, any deflection
amount may be used if it is within one pitch and the beams can also
be deflected towards shorter wavelengths.
In addition, spectroscopes shown in FIG. 5 and FIG. 7 to FIG. 9 are
presented as examples of the spectroscope. However, the present
invention can be adapted to all spectroscopes that use a PD array
system.
Although, in the spectrometers shown in FIG. 5 and FIG. 7 to FIG.
9, a configuration in which driver 42 applies a voltage to a
deflecting means based on the synchronizing signal of synchronizing
means 41 and driving means 43 reads the measured signal from PDM
16, a configuration without providing synchronizing means 41 may
also be used. In the configuration without providing synchronizing
means 41, it is arranged such that signals are exchanged between
driver 42 and driving means 43. For example, driver 42 applies a
voltage to a deflecting means, deflects measured light beams 100A
and 100B by a desired amount, and then outputs a signal to driving
means 43. Driving means 43 starts to read the measured signal from
PDM 16 based on the signal output from driver 42.
In the spectrometer shown in FIG. 7, an example, in which
piezoelectric actuator 52 is mounted so that it mechanically shifts
mirror 51 and in which a deflecting means is composed of mirror 51
and piezoelectric actuator 52, is shown. However, a configuration,
in which piezoelectric actuator 52 is attached to PDM 16 as a
moving means and the actuator moves PDM 16 in the arranging
direction of PD array by a desired amount, may be adopted. In such
a configuration, the moving means moves PDM 16 to change the
position where PDM 16 detects measured light beams 100A and
100B.
In the spectrometer shown in FIG. 8, a configuration in which
piezoelectric actuator 63 is used as a deflecting means is shown,
and in the spectrometer shown in FIG. 9, a configuration in which
electrodes 73a and 73b are used as a deflecting means is shown.
However, measured light beams 100A and 100B may be deflected by a
deflecting means which is composed of mirror 51 and piezoelectric
actuator 52 and placed in the optical path between grating area 61a
or 71a that emits the light beams and PDM 16 to which these light
beams are incident.
Further, although in the spectrometer shown in FIG. 8, a
configuration in which piezoelectric actuator 63 is used as a
deflecting means is shown, and in the spectrometer shown in FIG. 9,
a configuration in which electrodes 73a and 73b are used as a
deflecting means is shown, measured light beams 100A and 100B may
be deflected by electro-optic beam deflector 31 placed in the
optical path between grating area 61a or 71a that emits the light
beams and PDM 16 to which these light beams are incident.
Particularly in FIG. 8, this enables spectroscope 60 to operate
stably for a long time because mechanical moving parts are
removed.
According to the present invention, there are the following
effects:
Since a deflecting means deflects measured light beams and changes
the position where they are detected with a photodiode array,
measured signals equivalent to those obtained by measurement using
smaller pitch can be obtained without actually making the
photodiode pitch smaller. This enables the optical spot size of
measured light beams to be made smaller without using the data
whose detecting outputs are small and which are easily subjected to
influences of noise, and measurement can be performed with improved
wavelength resolution without being affected by the photodiode
pitch.
Since the deflecting means employs an electro-optic effect, the
spectroscope can be configured without including mechanical moving
parts. This enables the spectrometer to be operated stably for a
long time.
Since a moving means moves the photodiode array in the direction in
which obtaining the measured light beam spectrum is progressed and
changes the position where the beam is detected with the photodiode
array, measured signals equivalent to those obtained by measurement
using smaller pitch can be obtained without actually making the
photodiode pitch smaller. This enables the optical spot size of
measured light beams to be made smaller without using the data
whose detecting outputs are small and which are easily subjected to
influences of noise, and measurement can be performed with improved
wavelength resolution without being affected by the photodiode
pitch.
* * * * *